Abstract: A new hydrogenation method was introduced in an adiabatic fixed-bed reactor with gas and liquid upflow cocurrently. Three reaction regimes, i.e., liquid phase regime, mixed phase regime and gas phase regime were observed in the bed through regulating the operating conditions. Hydrogenation of benzene to cyclohexane over palladium catalyst was used as the model reaction. The effects of hydrogen flow rate, liquid flow rate, feed temperature and pressure on the flow regime were studied. For exothermic reactions, a small increase in reaction temperature can lead to a large increase in reaction rate due to Arrhenius temperature dependence of rate constant .The increased reaction rate results in more heat generation which further increases reaction temperature, this may results in reactor runaway. In this work, we propose that it is possible to obtain effective temperature control by using a fixed-bed reactor with cocurrent upflow of the reagents. The reaction heat evolved is absorbed by evaporation of the liquid phase. The experiments showed that the conversion of benzene in the reactor with this new kind of operation could reach almost 100%, and the risk due to hot spots appearance may also be avoided.